甘薯过氧化物酶的特性和抑制作用研究

研究甘薯过氧化物酶最适温度、最适pH值、Km及Vmax,同时探讨了不同激活剂和抑制剂对甘薯过氧化物酶的作用.结果表明:甘薯过氧化物酶最适温度为60℃,最适PH值为6.5,Km=0.00315293mol/L,Vmax=857372U/(min·g).抑制作用强弱依次为VC ＞L-cys＞NaHSO3＞柠檬酸＞EDTA,说明各抑制剂均具有一定的抑制作用.     

干燥条件对啤酒花品质的影响

研究了不同干燥温度和干燥时间对青岛大花烘烤过程中水分、α-酸、β-酸损失及酒花褐变度的影响。结果表明,在不同干燥温度条件下,随着干燥时间的延长,α-酸和β-酸均在逐渐减小,α-酸、β-酸的损失率逐渐增大,且α-酸的损失率大于β-酸的损失率。高温短时间干燥和低温长时间干燥均增大了α-酸、β-酸的损失率和褐变度,就α-酸和β-酸的损失率而言,70-60℃下,4-6h为最佳;对褐变度影响较小的温度是60℃和50℃。综上所述,对青岛大花品质影响最小的理想的干燥温度应确定为60℃左右为宜。     

绿茶罐装饮料的研制

本文研究绿茶罐装饮料的生产工艺，着重研究如何抑制绿茶罐装饮料常出现的色泽揭变、风味改变、白浊产生等问题。     

Kinetics of non-enzymatic browning in amorphous solid systems: distinguishing the effects of water activity and the glass transition

Debates have emerged recently on whether water activity or the state of the system as dictated by the glass transition temperature (T_g) impacts the rates of chemical reactions in reduced-moisture solid systems. The objective of this study was to evaluate the kinetics of brown pigment formation in polyvinylpyrrolidone model systems of different molecular weights so that the effects of water activity and the glass transition could be distinguished. Browning rates at different T_gs, but constant water activity, were significantly different except when all were in the glassy state. As the system changed from a glassy state to a rubbery state, the rate of browning increased 7-fold. The rate of browning also increased as water activity increased from 0.33 to 0.54, but then appeared to plateau with further increases in water activity. Thus, the rate of brown pigment formation is influenced significantly by the glass transition temperature of the system and less by the water activity. In addition, the concentration of reactants in the aqueous microenvironment had a significant impact on the rate of brown pigment formation.     

Effect of ultrafiltration on concentrated apple juice colour and turbidity

Colour and turbidity of conventional bentonite-gelatin clarified apple juice was compared with 30,000–50,000 and 100,000DA hollow fibre ultrafiltered apple juice, with and without pectinolytic enzyme treatment. Results indicated that objective quality of ultrafiltered apple juice compared favourably with conventionally clarified apple juice over 30 weeks of storage at 37.5°C. However, treatment with pectinolytic enzymes before ultrafiltration increased both the initial colour and the browning rate. No significant differences were found in the values of the transmission haze after storage.     

Quality Changes in Fresh-cut Pear Slices as Affected by Cultivar, Ripeness Stage, Fruit Size, and Storage Regime

Fresh-cut fruit slices prepared from partially ripened Bartlett pears had longer shelf life than those from Bosc, Anjou, and Red Anjou pears. Pear fruit ripeness, based on flesh firmness of 44 to 58 N, is optimal for fresh-cut pear slice processing. Pear slices derived from smaller size fruit (122 to 135 g) have greater cut surface discoloration and deteriorate more rapidly than slices derived from larger fruit (152 g). Recently harvested Bartlett pear fruit and whole pears held at –1 °C in a controlled atmosphere of 2%O₂+ 98%N₂ had a longer post-cutting shelf life than those held in air at –1 °C for the same duration. Cut surface browning, flesh softening, and surface dehydration of the slice cut surface were all contributors to loss of product quality.     

酶法水解梅鱼蛋白的实验研究

主要研究了碱性蛋白酶、风味蛋白酶、复合蛋白酶、中性蛋白酶对小梅鱼的水解作用。采用正交试验,详细比较了温度、酶浓度、水解时间、酶比例对鱼蛋白水解度的影响。结果表明:单酶最佳水解酶为碱性蛋白酶,其水解条件:温度60℃,加酶量0.3%(以蛋白含量计),时间5h,水解度达51.02%;碱性蛋白酶与复合蛋白酶双酶的最佳水解条件:碱性蛋白酶与复合蛋白酶比例为3∶1,温度为60℃,加酶量0.3%,时间5h,水解度达57.03%;碱性蛋白酶、复合蛋白酶与风味蛋白酶三酶的最佳水解条件:碱性蛋白酶与复合蛋白酶比例为3∶1,温度60℃,加酶量0.3%,反应5h后添加风味蛋白酶,其反应条件:加酶量0.3%,温度60℃,时间为6h,水解度达62.57%。     

当归愈伤组织褐化前后生理生化的研究

通过测定硝酸还原酶活力、可溶性蛋白质含量、还原糖含量以及丙二醛的含量来研究当归愈伤组织褐化前、后生理生化指标的变化;结果表明褐化对当归愈伤组织的活性影响显著。     

库尔勒香梨贮藏期间酶促褐变机理的研究

以贮藏后期的库尔勒香梨为研究对象，在一定的贮藏期内，定期对香梨中多酚氧化酶活性、酚类物质含量、过氧化物酶活性、丙二醛含量作测定。结果表明，香梨在贮藏期间先进行酚类物质合成，后发生降解，多酚氧化酶活性呈先升后降的趋势，丙二醛含量总体上升。     

Quantification of enzymatic browning kinetics in pear slices using non-homogenous L color information from digital images

A “fractal browning indicator” (FBI) methodology is presented, describing enzymatic browning based on irregular color patterns from digital pear slice surface images. It uses the Fourier fractal texture images to calculate a fractal dimension (FD) value in a selected area of the image, which represents the complexity of color distribution (lightness or L^∗) in the area analyzed. During the procedure, colors from digital images were first transformed to L^∗a^∗b^∗ space color using a transformation function, in order to derivate a lightness color parameter (L^∗). Experiments were carried out in three pear cultivars: Packham pear (PP); Hosui Asiatic pear (AP) and Berries Pear (BP). During the kinetics, the L^∗ decreased when the FD increased, indicating a greater complexity in the distribution of the L^∗ values in a selected analyzed area, during enzymatic browning kinetics, for all cultivars. The empirical power-law model was suitable for correlating enzymatic browning kinetics data both for the FBI and the traditional method (L^∗ mean value is used). However, enzymatic browning rates for PP cultivars, using the FBI method, were 25 times higher than the rates obtained with the traditional method; and 4 times higher for other cultivars respectively. The empirical non first-order model was established for all cultivars for the FBI and traditional methods.